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SubjectRe: [PATCH] [NETFILTER] bridge: rcu_deref outside read-lock section
On Tue, 14 Aug 2012 02:47:42 +0400
Denis Efremov <yefremov.denis@gmail.com> wrote:

> As it noted in the comment before the br_handle_frame_finish
> function, this function should be called under rcu_read_lock.
>
> The problem callgraph:
> br_dev_xmit -> br_nf_pre_routing_finish_bridge_slow ->
> -> br_handle_frame_finish -> br_port_get_rcu -> rcu_dereference
>
> And in this case there is no read-lock section.
> I have put lock/unlock in br_nf_pre_routing_finish_bridge_slow,
> as the only function that calls it(for now) - is br_dev_xmit.
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Denis Efremov <yefremov.denis@gmail.com>
> ---
> include/linux/netfilter_bridge.h | 6 +++++-
> 1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/netfilter_bridge.h b/include/linux/netfilter_bridge.h
> index 31d2844..ceb048e 100644
> --- a/include/linux/netfilter_bridge.h
> +++ b/include/linux/netfilter_bridge.h
> @@ -79,6 +79,7 @@ extern int br_handle_frame_finish(struct sk_buff *skb);
> /* Only used in br_device.c */
> static inline int br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
> {
> + int res;
> struct nf_bridge_info *nf_bridge = skb->nf_bridge;
>
> skb_pull(skb, ETH_HLEN);
> @@ -86,7 +87,10 @@ static inline int br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
> skb_copy_to_linear_data_offset(skb, -(ETH_HLEN-ETH_ALEN),
> skb->nf_bridge->data, ETH_HLEN-ETH_ALEN);
> skb->dev = nf_bridge->physindev;
> - return br_handle_frame_finish(skb);
> + rcu_read_lock();
> + res = br_handle_frame_finish(skb);
> + rcu_read_unlock();
> + return res;
> }
>
> /* This is called by the IP fragmenting code and it ensures there is

Why not just move the rcu_read_lock() in br_dev_xmit earlier?


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